1. Field of the Invention
The present invention relates to a method and device for mechanically imaging the prostate.
2. Description of Related Art
Conventional methods for early detection of prostate cancer include digital rectal examination (DRE). Digital rectal examination or palpation, that is an examination using the sense of touch, is based on the significant differences in elasticity of normal tissues and certain lesions. Palpation has been a commonly used test by general practitioners and specialists and is recommended as a part of an annual general preventive physical examination for all men 40 years of age and older. The effectiveness and reliability of palpation is dependent on the level of skill of the examiner, since the finger as an instrument does not provide any quantitative information, and therefore the examiner must instinctively relate what he/she senses by the finger to their previous experience with palpation, as described in Littrup et al., The Benefit and Cost of Prostate Cancer Early Detection, CA Cancer Journ. for Clinicians, Vol. 43, pp. 134-149 (1993). It has been found that the disagreement between the palpatory findings of experienced urologists is about 20%, as described in Smith et al., Interexaminer Variability of Digital Rectal Examination in Detecting Prostate Cancer, Urology, Vol. 45, pp. 70-74 (1995). The disagreement within inexperienced examiners (who are most likely to carry the bulk of cancer screening) is much higher. Once a lesion is palpated, documentation of the abnormality depends on the precision of a physician's description or a freehand diagram.
Several authors have proposed various types of devices mimicking palpation to detect tumors using different types of pressure sensors. For example Frei et al., U.S. Pat. No. 4,250,894, have proposed an instrument for breast examination that uses a plurality of spaced piezoelectric strips which are pressed into the body being examined by a pressure member which applies a given periodic or steady stress to the tissue beneath the strips.
Another approach to evaluate the elasticity of the tissues uses indirect means, such as conventional imaging modalities (ultrasound or MRI) which are capable of detecting motion of a tissue subjected to an external force. One approach attempts to determine the relative stiffness or elasticity of tissue by applying ultrasound imaging techniques while vibrating the tissue at low frequencies. See, e.g., J. J. Parker et al., U.S. Pat. No. 5,099,848; R. M. Learner et al., Sono-Elasticity: Medical Elasticity Images Derived From Ultrasound Signals in Mechanically Vibrated Targets, Acoustical Imaging, Vol. 16, 317 (1988); T. A. Krouskop et al., A Pulsed Doppler Ultrasonic System for Making Non-Invasive Measurement of Mechanical Properties of Soft Tissue, 24 J. Rehab. Res. Dev. Vol. 24, 1 (1987); Y. Yamakoshi et al., Ultrasonic Imaging of Internal Vibration of Soft Tissue Under Forced Vibration, IEEE Transactions on Ultrasonics Ferroelectrics, and Frequency Control, Vol. 7, No. 2, Page 45 (1990).
Sarvazyan et al., have developed a device for elasticity imaging of the prostate using an ultrasonic transrectal probe (U.S. Pat. No. 5,265,612). This device enables physicians to quantitatively and objectively characterize elasticity moduli of prostate tissues. The elasticity characterization and imaging is achieved by evaluating the pattern of the internal strain in the prostate and surrounding tissues using conventional transrectal ultrasonography. The pattern of internal strain is obtained by ultrasonically imaging the prostate at two levels of its deformation. The deformation is provided by changing the pressure in the fluid filling the sheath surrounding the transrectal probe. In addition to elasticity, other tumor parameters reflecting the stage of its development include the geometrical parameters of the tumor, such as its volume or diameter. Lacoste et al., U.S. Pat. No. 5,178,148, have disclosed a method of determining the volume of a tumor or gland, particularly the prostate, using an endocavity detector probe, in particular, a transrectal probe.
It has been described that the combination of palpation and detection by using prostate specific antigen (PSA) almost doubles the cancer detection rate, see Catalona et al., A Multicenter Evaluation of PSA and Digital Rectal Examination (DRE) for Early Detection of Prostate Cancer in 6,374 Volunteers, J Urol, Vol. 149 (Suppl), p. 412 (1993). The combined method is recommended by the American Urological Association and American Cancer Society, and was recently approved by FDA for screening patients between ages of 50 and 75 years old. It was demonstrated that a combined-modality approach to prostate cancer detection yields high levels of early detection with infrequent adverse outcomes, since palpation detects cancer that would otherwise be missed by PSA measurements.
It is desirable to provide an improved method and device for palpation and mechanical imaging of the prostate.